Overdrive issues on '91

[pankodog]

This pup doesn't like to stay in overdrive unless conditions are just right- I maintain the tranny- change fluid and filter yearly- other than that it shifts and runs well.

 

[MrShorty]

3-4 shift and torque converter lockup are both controlled by the PCM. Which one (or both?) is shifting when it shouldn't? 1st thing I'd probably do would be to determine if it is a question of control (an electrical fault or something in the engine management system). These are fairly straightforward DC circuits, so it isn't overly difficult to check them if you have a DVOM and a wiring diagram.